Samson Grey has some good suggestions in his latests vids (
https://www.youtube.com/@SamsonGrey26/videos) but I thought of a fewmore:
Right Now:
If you are going to try Viper and/or Pictomancer, start building a L80 Poetics gearset for those jobs (SCOUTING/DEX for Viper, CASTING/INT for Picto). If you're like me, you're capped on Poetics, and this will be the best possible gear to start the new classes on. If you're short on Poetics, get the right-hand side (accessories): you'll probably be given the weapon and left-hand side when you pick up the class.
DoH/Dol: Unlock and get to max rep as many Custom Delivery targets as you can: Custom Delivery gives massive amounts of XP for minimal effort, and that XP is even larger if the delivery target is offering a bonus, which are only offered once you get max affection. Having more delivery targets at max affection gives you a better chance of getting a bonus for the crafter or gatherer you are trying to level.
DoH: clean up your inventory to make room for the new mats you'll need.
Rank up your Adventurer Squadron and run Priority Missions to get Squadron Manuals: you can run one Priority Mission a week, and the rewards for success can be 5 or 10 Squadron Battle, Survival, or Engineering Manuals (among others). These give a 15% XP boost for combat (Battle) or a 20% XP boost to crafting (Engineering) or gathering (Survival) for two hours. They do
not stack with FC buffs like Heat of Battle II.
Tip of the hat to NekiUno.
Immediately Pre-launch/Pre-Early Access:
In the week before whichever marks your starting point, get, complete but do not turn in a Wondrous Tales book: These books can be turned in the week after you get them, and then you can get a second book. So if you are getting Early Access, sometime in June 18-24, pick up a book, get it complete, turn it in on June 28, pick up another on June 28, complete it and turn it in before July 2, and then on July 2 pick up a third book, complete it and turn it in. This should give you 1.5 levels of XP on a combat class of your choice.